The present project is designed in two parts. The first part is a prevalence study of behavior problems in the total population of three year-old children living in families of permanent residents on the Island of Martha's Vineyard. Behavior problems are determined with the Behavior Screening Questionnaire of Richman and Graham, a twelve-item parent questionnaire. The reliability of this instrument is extended to include a comparison of the reports of fathers and mothers of the children. The validity of the questionnaire is improved by comparing the reports of parents with an interview with the child. Following this study a two year prospective longitudinal study is carried out in the same community. The purpose of this investigation is to examine the influence of temperamental characteristics of children and stressful life events in families as predictors of behavior problems.